Picowatt, 0.45-0.6 V Self-Biased Subthreshold CMOS Voltage Reference

In this paper, a self-biased temperature-compensated CMOS voltage reference operating at picowatt-level power consumption is presented. The core of the proposed circuit is the self-cascode MOSFET (SCM) and two variants are explored: a self-biased SCM (SBSCM) and a self-biased NMOS (SBNMOS) voltage reference. Power consumption and silicon area are remarkably reduced by combining subthreshold operation with a self-biased scheme. Trimming techniques for both circuits are discussed aiming at the reduction of the process variations impact. The proposed circuits were fabricated in a standard 0.18-mu m CMOS process. Measurement results from 24 samples of the same batch show that both circuits herein proposed can operate at 0.45/0.6 V minimum supply voltage, consuming merely 55/184 pW at room temperature. Temperature coefficient (TC) around 104/495 ppm/degrees C across a temperature range from 0 to 120 degrees C was measured. Employment of a trimming scheme allows a reduction of the average TC to 72.4/11.6 ppm/degrees C for the same temperature range. Both variants of the proposed circuit achieve a line sensitivity of 0.15/0.11 %/V and a power supply rejection better than -44/-45 dB from 10 to 10 kHz. In addition, SBSCM and SBNMOS prototypes occupy a silicon area of 0.002 and 0.0017 mm(2), respectively.